Patent GB-1465181-A (GB)
Title: Apertured-mask cathode-ray tube
IPC: H01J9/22
Filed: 1974-02-04
Abstract: 1465181 Colour cathode ray tube display tubes RCA CORPORATION 4 Feb 1974 [5 Feb 1973] 5116/74 Heading H1D A colour c.r.t. has an apertured mask and a phosphor mosaic viewing screen with a half-tone pattern of heat absorbing material and heat reflecting material. The half-tone pattern is defined to mean any pattern of dots or lines on a contrasting background wherein the pattern or background is formed of heat absorbing material and the other is of heat reflecting material. Heat transfer from the mask to the screen and the electron beam attenuation characteristic may then be controlled. The pattern may be dots of dark coloured material on a heat reflecting A1 layer, the dots being registered with the phosphor areas and graded in size with the largest areas at the screen central portion. Heat absorbing areas may overlap in the central area for example, and may be larger than the phosphor areas at the central portion and the same size at the edge, or may be the same size at the central portion and smaller at the edge, or may be larger and smaller at the centre and periphery respectively. The heat absorbing pattern need not follow the phosphor pattern and the thickness may be uniform or graded to provide the required heat transfer. The pattern may be heat reflecting dots surrounded by heat absorbing material. Heat reflectors may be vapour deposited Al, aluminium oxide, titanium oxide or magnesium oxide, reference being also made to smooth, shiny and metallic, and also smooth and/or light coloured surfaces. Infra-red absorbers may be rough or matte black finish, or may be rough and/or dark coloured, optimally at least 1/10 the thickness of the peak emission wavelength from a black body, e.g. 8440 nm. at 80 C. Coatings may be black particles, e.g. graphite, carbon, manganese dioxide, nickel oxide and black iron oxide. Lithium nitride, boron carbide and nickel oxide are also mentioned in the prior art discussion. Brown, grey, blue, green and purple coloured materials may be used, and such as in U.S.A. Specification 3,392,397. Figs. 3 to 6 (not shown), indicate loci for equal sized areas, some dimensions being given. The half-tone pattern need not follow the phosphor pattern. Fabrication is by reference to publications. Photo-deposition of C particles may use p.v.a. photo-sensitive binder and mask or photographic master with a neutral graded filter. When the heat absorbing pattern surrounds the heat reflecting areas, a positive photo-binder is used. The photo-binder alternatively carries a salt heat-decomposable to a heat absorbing material (e.g. manganous oxalate or manganous carbonate). Fig. 1 (not shown), includes an electrically conductive coating 17 of heat absorbing material (e.g. graphite particles in a silicate binder), heat absorbing areas (33) of carbon particles, mask (35) of cold rolled steel blackened on both sides by oxidation, and gun assembly (23) producing three beams. There is also reference to shadow mask tubes with one or more electron beams, and phosphors are exemplified. Phosphor areas may be lines, round, oval or rectangular.